1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor (hereinafter, sometimes simply referred to as a “photoreceptor”), and more specifically, relates to an electrophotographic photoreceptor applied to an image forming apparatus using an electrophotographic system, such as a printer, a copying machine and a facsimile machine.
2. Background of the Related Art
An electrophotographic photoreceptor has a basic structure containing an electroconductive substrate having provided thereon a photosensitive layer. As the electrophotographic photoreceptor, an organic electrophotographic photoreceptor using an organic photoconductive substance has been proposed in a large number of reports and is being applied to practical use from the standpoint of pollution prevention, reduction in cost, and flexibility of material selection, by which the characteristics of the photoreceptor can be variously designed.
A photosensitive layer of the organic photoreceptor contains a layer mainly having an organic photoconductive substance dispersed in a resin, and various proposals have been made, which include a layered structure containing a layer having a charge generating substance dispersed in a resin (charge generation layer) and a layer having a charge transporting substance dispersed in a resin (charge transport layer) laminated thereon, and a single layer structure having a charge generating substance and a charge transporting substance dispersed in a resin.
In general, an electrophotographic photoreceptor is required to have sensitivity, electrical characteristics and optical characteristics that are demanded in an electrophotographic process, to which the photoreceptor is applied. Furthermore, in a photoreceptor to be used repeatedly, the outermost layer of the photoreceptor, i.e., the layer farthest from the electroconductive substrate, is directly applied with electrical and mechanical external forces, such as corona charging, development with a toner, transfer to paper, and cleaning, and thus the layer is required to have durability thereto. Specifically, it is required to have durability to wear and formation of scratches on the surface due to friction with another member, and deterioration of the surface due to ozone formed upon corona charging. In particular, since the service life of the electrophotographic photoreceptor largely depends on wear of the surface thereof, it is necessary to suppress scratching of the surface layer. There is another problem of adhesion of toner (filming) on the surface of the photoreceptor due to repetition of development with a toner and cleaning. Filming should be prevented from occurring since an image defect occurs in an area where filming occurs. In order to prevent filming from occurring, it is necessary to improve the cleaning properties of the surface of the photoreceptor.
For this purpose, an attempt was made to add a lubricating component to a surface layer of a photoreceptor to improve the surface lubricating property and to reduce an adhesion force of toner to the surface, whereby the toner is prevented from adhering to suppress filming from occurring. However, when a liquid lubricant is used, it is poor in maintenance of its effect upon repeated use, and when a solid lubricant is used, it has problems in dispersibility and stability of a coating composition.
As a technique relating to improvement in surface properties of a photoreceptor, for example, JP-A-10-171135 discloses an electrophotographic photoreceptor having a photosensitive layer containing a prescribed silicone oil in a prescribed amount, so as to realize a photoreceptor that is excellent in wear resistance upon repeated use, is capable of reducing surface energy of the photoreceptor, and for which toner filming and background contamination is prevented. However, while the technique provides lubricating properties to the surface by dispersing silicone oil in the photosensitive layer, the silicone oil separates out on the surface of the photoreceptor and, thus, it is difficult to maintain the lubricating properties upon repeated use so that insufficient durability results.
It has been known to apply the technique of microcapsules to an electrophotographic photoreceptor. A microcapsule is a minute capsule having a size on the order of a micrometer. As a technique relating to a photoreceptor using microcapsules, JP-A-60-256149 discloses an electrophotographic photoreceptor having a photoconductive layer containing a powder of a phthalocyanine photoconductive material and a sensitizing agent, which have been microencapsulated with a resin, so as to improve the ozone resistance and the humidity resistance without deterioration in sensitivity.
JP-A-6-3848 discloses that upon forming a color image using photosensitive microcapsules containing a color toner, a light scattering material is attached to the photosensitive microcapsules in different amounts respectively, whereby an image having color reproducibility truthful to the original image can be obtained. JP-A-2001-290295 discloses addition of a wear preventing material which has been treated with a prescribed resin, preferably microencapsulated, to the outermost layer of a photoreceptor, whereby the wear resistance on the surface of the photoreceptor is improved, and the residual potential thereon is lowered.
JP-A-8-305171 discloses a developer carrying member having a one-component developer (toner) carried thereon, a thin film constituted by a binder resin and releasing agent-containing capsule particles containing a releasing agent as a core substance formed on the surface thereof. A developer carrying member results which provides improved wear resistance of the film on the surface of the developer carrying member, which is stable in surface roughness and charge imparting property to the toner, which is suppressed in occurrence of excessive charging of the toner and fusion of the toner onto the developer carrying member and a photoreceptor drum, and which is suppressed in occurrence of decrease in image density.